The Nine Genes of the Nocardia lactamdurans Cephamycin Cluster Are Transcribed into Large mRNAs from Three Promoters, Two of Them Located in a Bidirectional Promoter Region

The nine biosynthesis genes of the Nocardia lactamdurans cephamycin cluster are expressed as three different mRNAs initiating at promoters latp, cefDp, and pcbABp, as shown by low-resolution S1 nuclease protection assays and Northern blotting analysis. Bidirectional expression occurred from divergent promoters (latp and cefDp) located in a 629-bp intergenic region that contains three heptameric direct repeats similar to those recognized by members of the SARP (Streptomyces antibiotic regulatory proteins) family. The lat gene is transcribed in a single monocistronic transcript initiating at latp. A second unusually long polycistronic mRNA (more than 16 kb) corresponding to six biosynthesis genes (pcbAB, pcbC, cmcI, cmcJ, cefF, and cmcH) started at pcbABp. A third polycistronic mRNA corresponding to the cefD and cefE genes started at cefDp.